The invention relates to an actuator for an electrohydraulic gas-exchange valve train of a combustion engine. The actuator comprises an actuator housing that can be mounted on the combustion engine that includes a borehole, a hydraulic piston supported so that it can move in this borehole for actuating the gas-exchange valve, and an axial stop that restricts the piston stroke out of the borehole to a mounting stroke in the unmounted state of the actuator housing on the combustion engine.
For electrohydraulic valve trains, the variability of the control times and the maximum stroke on the gas-exchange valve is produced in a known way such that, between a cam of a camshaft and the gas-exchange valve, a so-called hydraulic linkage with a compression chamber is arranged whose volume can be regulated in a continuously variable way by an electromagnetic hydraulic valve in a pressure-relief chamber. Depending on the regulated volume of the hydraulic medium, the cam stroke specified by the camshaft is then converted completely, partially, or not at all into a stroke of the gas-exchange valve.
The present invention relates to the gas-exchange-valve-side part of the valve train actuator system whose movement corresponds to the stroke of the gas-exchange valve and is known, for example, from DE 10 2010 048 135 A1 according to the class. In the unmounted state of the actuator housing, the hydraulic piston does not sit on the gas-exchange valve and can move out of the borehole of the actuator housing under the effect of the force of gravity. This extension stroke is limited by an axial end stop to a mounting stroke in order to prevent the hydraulic piston from falling out of the borehole during the mounting of the actuator on the combustion engine.
The mounting stroke is not only to be dimensioned to the effect that the hydraulic piston does not fall out of the borehole before and during the mounting of the actuator housing, but also such that the end side of the extended hydraulic piston is always set with sufficient overlap on the end side of the gas-exchange-valve shaft, in order to prevent lateral placement or sliding of the hydraulic piston onto the circumference of the valve shaft. The risk of such incorrect mounting deforming the components increases if the gas-exchange valve is inclined—as is typical—toward the mounting direction of the actuator housing, and that is with increasing mounting stroke and increasing angle of inclination.